Image information decoding apparatus and image information decoding method for motion prediction and/or compensation of images

ABSTRACT

The present invention is directed to an image information encoding apparatus, used in receiving compressed image information through network media when processing of such compressed image information is performed on storage media. A picture sorting buffer delivers information of picture type of frame Picture_type to a picture type discrimination unit. The picture type discrimination unit transmits command to a motion prediction/compensation unit on the basis of that information. The motion prediction/compensation unit generates predictive picture by using filter coefficients having the number of taps lesser than that of P picture with respect to B picture for which operation quantity and the number of memory accesses are required to more degree as compared to P picture on the basis of that command.

CROSS-REFERENCE TO RELATED APPLICATIONS

This present application is a Divisional application of application Ser.No. 10/501,714 filed Mar. 2, 2005, which is a National Stage ofPCT/JP03/00606, filed Jan. 23, 2003, and claims the benefit of priorityfrom Japanese Application No. 2002-14888 filed Jan. 23, 2002, theentirety of both of which is incorporated by reference therein.

TECHNICAL FIELD

The present invention relates to an image information encoding apparatusand a method therefor, an image information decoding apparatus and amethod therefor, and a program which are used in receiving, throughnetwork media such as satellite broadcast, cable TV and/or Internet,etc., or in processing on storage media such as optical disc, magneticdisc or flash memory, etc. compressed image information (bit stream) byorthogonal transform such as discrete transform or Kamen-Loevetransform, etc. and motion compensation like MPEG (Moving PictureExperts Group), H.26x,

BACKGROUND ART

In recent years, apparatuses in conformity with the system such as MPEGin which image information is handled as digital information tocompress, in that instance, image information by orthogonal transformsuch as discrete cosine transform, etc. and motion compensation bymaking use of redundancy specific to image information for the purposeof performing transmission and/or storage of efficient information arebeing popularized in both information distribution (delivery) atbroadcast station, etc. and information reception in general homes.

Particularly, MPEG 2 (ISO/IEC 13818-2) is defined as general purposeimage encoding system, and is widely used at present for broadapplications of professional use purpose and consumer use purpose at thestandard where both interlaced scanning image and sequential scanningimage, and standard resolution image and high definition image arecovered or included. By using the MPEG 2 compression system, e.g., inthe case of interlaced scanning image of standard resolution having720×480 pixels, code quantity (bit rate) of 4 to 8 M bps is assigned,and in the case of interlaced scanning image of high resolution having1920×1088 pixels, code quantity (bit rate) of 18 to 22 M bps is assignedso that high compression factor and satisfactory picture quality can berealized.

The MPEG 2 was mainly directed to high picture quality encoding adaptedfor broadcast, but did not comply with code quantity (bit rate) lowerthan the MPEG 1, i.e., encoding system of higher compression factor.However, it is expected that need of such encoding system will beincreased in future by popularization of portable terminals. Incorrespondence therewith, standardization of the MPEG 4 encoding systemwas performed. In regard to the image encoding system, the standardthereof was approved for the International standard as ISO/IEC 14496-2in December, 1998.

Further, in recent years, for the first object of image encoding fortelevision conference, the standardization of H.26L (ITU-T Q6/16 VCEG)is being developed. At H.26L, it is known that while a larger number ofoperation quantities are required in encoding/decoding therefor ascompared to the conventional encoding system of the MPEG 2 or MPEG 4,higher encoding efficiency can be realized. Moreover, at present, as apart of activity of MPEG 4, standardization in which functions whichcannot be supported by the H.26L are also taken in with such H.26L beingas base is being performed as Joint Model of Enhanced-Compression VideoCoding.

Meanwhile, in the H.26L, as one of element technology for realizing highencoding efficiency, motion prediction/compensation based on variableblock is mentioned. Under existing circumstances, seven kinds ofprediction/compensation block sizes as shown in FIG. 1 are determined.

Moreover, in the H.26L, motion prediction/compensation processing ofhigh accuracy such as 1/4 pixel accuracy or 1/8 pixel accuracy areprescribed. In the following description, motion prediction/compensationprocessing will be first described.

The motion prediction/compensation processing of 1/4 pixel accuracydetermined in the H.26L is shown in FIG. 2. In generating predictivepicture of 1/4 pixel accuracy, FIR filters respectively having 6 taps inhorizontal and vertical directions are first used to generate pixelvalues of 1/2 pixel accuracy on the basis of pixel values stored in theframe memory. Here, as coefficients of the FIR filter, coefficientsindicated by the following formula (1) are determined.{1, −5, 20, 20, −5, 1}/32  (1)

Further, predictive picture of 1/4 pixel accuracy is generated by linearinterpolation on the basis of the generated predictive picture of 1/2pixel accuracy.

Further, at the H.26L, for the purpose of performing motionprediction/compensation of 1/8 pixel accuracy, filter banks shown in thefollowing formula (2) are prescribed.1:11/8: {−3, 12, −37, 485, 71, −21, 6, −1}/5122/8: {−3, 12, −37, 229, 71, −21, 6, −1}/2563/8: {−6, 24, −76, 387, 229, −60, 18, −4}/5124/8: {−3, 12, −39, 158, 158, −39, 12, −3}/256  (2)5/8: {−4, 18, −60, 229, 387, −76, 24, −6}/5126/8: {−1, 6, −21, 71, 229, −37, 12, −3}/2567/8: {−1, 6, −21, 71, 485, −37, 12, −3}/512

It is to be noted that, in the image compressed information, accuracy ofmotion vector is prescribed by MotionRelation field in RTP (Real-timeTransfer Protocol).

As stated above, in the existing H.26L, motion prediction/compensationprocessing using a filter determined in advance as shown in the formula(1) or (2) is prescribed. In addition, as described in “AdaptiveInterpolation Filter for Motion Compensated Hybrid Video Coding” T.Wedi, Picture Coding Symposium 2001, pp 49-52 (hereinafter referred toas literature 1), it is also being considered at present to use adaptivefilter corresponding to input image is used.

In concrete terms, in the literature 1, adaptive optimization for motionprediction compensation processing as described below is proposed.Namely, initially, as the first step, a filter determined in advance isused to determine motion vector d(k) which minimizes predictive error.Subsequently, as the second step, filter coefficients H(k) such thatpredictive error is minimized with respect to the motion vector d(k)determined at the first step are determined. By the filter coefficientsH(k) and the motion vector d(k) which have been determined in this way,motion compensation processing is performed. In accordance with theliterature 1, in the simulation experiment using test sequence “Mobile2and “Foreman”of CIF size, encoding gain of the order of 1.0 to 1.5 dBcan be obtained by the above-mentioned technique as compared to the casewhere filter determined in advance is used.

Here, in the H.26L, similarly to the MPEG 2, prescription relating to Bpicture is included. A method for bi-directional prediction using Bpicture in the H.26L is shown in FIG. 3. As shown in FIG. 3, B₂ pictureand B₃ picture use I₁ picture and P₄ picture as reference picture, andB₅ picture and B₆ picture use P₄ picture and P₇ picture as referencepicture.

Moreover, in the image compressed information, uses of respectivepictures are prescribed as shown in FIG. 4 by PTYPE in the pictureheader. As shown in FIG. 4, when value of Code number is 0 or 1, use ofP picture is designated. When value of Code number is 2, use of Ipicture is designated. When value of Code number is 3 or 4, use of Bpicture is designated. In this instance, when value of Code number is 0,only picture immediately before is used for prediction, whereas whenvalue of Code number is 1, plural past pictures are used for prediction.Further, when value of Code number is 3, pictures immediately before andimmediately after are used for prediction, whereas when value of Codenumber is 4, plural past and future pictures are used for prediction. Asstated above, similarly to the P picture, also in the B picture,multiple frame prediction can be used.

Further, in the H.26L, B picture is used to thereby permit realizationof time scalability. Namely, since there is no possibility that Bpicture is used as reference range, B picture can be annulled withoutperforming its decoding processing.

Furthermore, in the B picture, five kinds of predictive modes of directpredictive mode, Forward predictive mode, Backward predictive mode,Bi-directional predictive mode and intra predictive mode are prescribed.It is to be noted that while the direct predictive mode and thebi-directional predictive mode are both bi-directional prediction,difference therebetween is that different motion vector information areused in the forward direction and in the backward direction in thebi-directional predictive mode, whereas motion vector information of thedirect predictive mode is read out from corresponding macro block in thefuture predictive frame.

Macro block type (MB_Type) with respect to B picture prescribed in theH.26L is shown in FIG. 5. Here, in FIG. 5, Forward of columns ofrespective Prediction Types corresponding to Code_number indicates typeof forward direction, Backward thereof indicates type of backwarddirection, Bi-directional thereof indicates type of bi-direction, andintra thereof indicates type within picture (frame), and the descriptionsuch as “16×16”succeeding thereto indicates size of prediction block asshown in FIG. 1. Moreover, information to which “X”is attached ofrespective columns of intra_pred_mode Ref_frame, Blk_size MVDFW andMVDBW are defined with respect to corresponding Prediction Types. Forexample, MVDFW and MVDBW respectively indicate forward motion vectorinformation and backward motion vector information. In addition, withrespect to information of field block size Blk_size in theBi-directional mode, the relationship between Code_number and Block Sizeas shown in FIG. 6 is prescribed.

However, in a manner as shown in FIG. 3, in the B picture,bi-directional prediction is used to thereby realize higher encodingefficiency as compared to I/P pictures, but a larger number of operationquantities and memory accesses are required as compared to the I/Ppictures.

Particularly, in the case where the H.26L system is used, sinceinterpolation processing using filter of 6 taps or 8 taps as indicatedby the formula (1) or (2) is performed in prediction/compensationprocessing, there was the problem that its operation quantity and thenumber of memory accesses becomes vast as compared to the case where theMPEG 2 system is used.

DISCLOSURE OF THE INVENTION

The present invention has been proposed in view of conventional actualcircumstances as described above, and its object is to provide an imageinformation encoding apparatus a method therefor, an image informationdecoding apparatus and a method therefor, and a program which areadapted for reducing operation quantity and the number of memoryaccesses in motion prediction/compensation processing with respect to Bpicture.

The image information encoding apparatus according to the presentinvention is directed to an image information encoding apparatus adaptedfor encoding an input image signal at least including intraframeencoding image, interframe forward prediction encoding image andinterframe bi-directional encoding image by orthogonal transform andmotion prediction/compression processing in which plural different pixelaccuracies can be selected to generate image compressed information, theimage information encoding apparatus comprising motion/predictioncompensation means for performing motion prediction/compressionprocessing based on different interpolation methods with respect tointerframe forward prediction encoding image and interframebi-directional prediction encoding image.

Here, the motion prediction compensation means selects, as aninterpolation method with respect to interframe bi-directionalprediction encoding image, a method in which operation quantity and thenumber of memory accesses are reduced as compared to the interframeforward prediction encoding image.

The image information encoding apparatus according to the presentinvention further comprises picture type discrimination means fordiscriminating picture type of an input image signal, wherein thepicture type discrimination means transmits, to motionprediction/compensation means, command corresponding to interframeforward encoding image or interframe bi-directional predictive encodingimage in accordance with discrimination result of picture type tocontrol the command.

Such image information encoding apparatus discriminates picture type ofan input image signal to perform, with respect to interframebi-directional prediction encode image, motion prediction/compensationprocessing based on an interpolation method in which operation quantityand the number of memory accesses are reduced to more degree as comparedto interframe forward prediction image to thereby reduce operationquantity and the number of memory accesses in motionprediction/compensation processing.

The image information encoding method according to the present inventionis directed to an image information encoding method of encoding an inputimage signals at least including intraframe encoding image, interframeforward prediction encoding image and interframe bi-directionalprediction encoding image by orthogonal transform and motionprediction/compensation processing in which plural different pixelaccuracies can be selected to generate image compressed information, theimage information encoding method including a motionprediction/compensation step of performing motionprediction/compensation processing based on different interpolationmethods with respect to interframe forward prediction encoding image andinterframe bi-direction prediction encoding image.

Here, at the motion prediction/compensation step, as an interpolationmethod with respect to interframe bi-directional prediction encodingimage, there is selected a method in which operation quantity and thenumber of memory accesses are reduced to more degree as compared tointerframe forward prediction encoding image.

The image information encoding method according to the present inventionfurther includes a picture type discrimination step of discriminatingpicture type of an input image signal, wherein, at the picture typediscrimination step, transmission of command corresponding to interframeforward prediction encoding image or interframe bi-directionalprediction encoding image is performed in accordance with discriminationresult of picture type so that processing at the motionprediction/compensation step is controlled.

In such image information encoding method, picture type of input imagesignal is discriminated so that motion prediction/compensationprocessing based on interpolation method in which operation quantity andthe number of memory accesses are reduced to more degree as compared tointerframe forward prediction encoding image is performed with respectto interframe bi-directional predictive encoding image so that operationquantity and the number of memory accesses are reduced in motionprediction/compensation processing.

The program according to the present invention is directed to a programfor allowing computer to execute processing which encodes an input imagesignal at least including intraframe encoding image, interframe forwardprediction encoding image and interframe bi-directional predictionencoding image by orthogonal transform and motionprediction/compensation processing in which plural different pixelaccuracies can be selected to generate image compressed information, theprogram including a motion prediction/compensation processing based ondifferent interpolation methods with respect to interframe forwardprediction encode imaging and interframe bi-directional predictionencoding image.

Here, at the motion prediction compensation step, as an interpolationmethod with respect to interframe bi-directional prediction encodingimage, there is selected a method in which operation quantity and thenumber of memory accesses are reduced to more degree as compared tointerframe forward prediction encoding image.

The program according to the present invention further includes apicture type discrimination step of discriminating picture type of aninput image signal, wherein, at the picture type discrimination step,transmission of command corresponding to interframe forward predictionencoding image or interframe bi-directional prediction encoding image isperformed in accordance with discrimination result of picture type sothat processing at motion prediction/compensation step is controlled.

Such a program allows computer to discriminate picture type of an inputimage signal to perform prediction/compensation processing based on aninterpolation method in which operation quantity and the number ofmemory accesses are reduced to more degree as compared to interframeforward predictive encoding image to thereby reduce operation quantityand the number of memory accesses in motion prediction/compensationprocessing.

The image information decoding apparatus according to the presentinvention is directed to an image information decoding apparatus adaptedfor decoding image compressed information at least including intraframeencoding image, interframe forward prediction encoding image andinterframe bi-directional prediction encoding which have been generatedat an image information encoding apparatus by inverse orthogonaltransform and motion prediction/compensation processing in which pluraldifferent pixel accuracies can be selected, the image informationdecoding apparatus comprising motion prediction/compensation means forperforming motion prediction/compensation processing based on differentinterpolation methods with respect to interframe forward predictionencoding image and interframe bi-directional prediction encoding image.

Here, the motion prediction/compensation means selects, as aninterpolation method with respect to interframe bi-directionalprediction encoding image, a method in which operation quantity and thenumber of memory accesses are reduced to more degree as compared tointerframe forward prediction encoding image.

The image information decoding apparatus according to the presentinvention further comprises picture type discrimination means fordiscriminating picture type of image compressed information, wherein thepicture type discrimination means performs transmission of interframeforward prediction encoding image or interframe bi-directionalprediction encode imaging in accordance with discrimination result ofthe picture type to control the command.

Such an image information decoding apparatus discriminates picture typeof image compressed information generated in an image informationencoding apparatus to perform motion prediction/compression processingbased on an interpolation method in which operation quantity and thenumber of memory accesses can be reduced to more degree as compared tointerframe forward prediction encoding image to thereby reduce operationquantity and the number of memory accesses in motionprediction/compression processing.

The image information decoding method according to the present inventionis directed to an image information decoding method of decoding imagecompressed information at least including intraframe encoding image,interframe forward prediction encoding image and interframebi-directional prediction encoding image by inverse orthogonal transformand motion prediction/compensation processing in which plural differentpixel accuracies can be selected, the image information decoding methodincluding motion prediction/compensation step of performing motionprediction/compensation processing based on different interpolationmethods with respect to interframe forward prediction encoding image andinterframe bi-directional prediction encoding image.

Here, at the motion prediction/compensation step, as an interpolationmethod with respect to interframe bi-directional prediction encodingimage, there is selected a method in which operation quantity and thenumber of memory accesses are reduced to more degree as compared tointerframe forward prediction encoding image.

The image information decoding method according to the present inventionfurther includes a picture type discrimination step of discriminatingpicture type of image compressed information, wherein, at the picturetype discrimination step, transmission of command corresponding tointerframe forward predictive encoding image or interframebi-directional prediction encode imaging is performed in accordance withdiscrimination result of the picture type so that processing at themotion/compression is controlled.

In such image information decoding method, picture type of imagecompressed information generated at the image information encodingapparatus is discriminated, and motion prediction/compensationprocessing based on an interpolation method in which operation quantityand the number of memory accesses are reduced to more degree as comparedto the interframe forward prediction encoding image so that operationquantity and the number of memory accesses in motionprediction/compensation processing are reduced.

The program according to the present invention is directed to a programfor allowing computer to execute processing which decodes imagecompressed information at least including intraframe encoding image,interframe forward prediction encoding image and interframebi-directional prediction encoding image which have been generated at animage information encoding apparatus by inverse-orthogonal transform andmotion prediction/compensation processing in which plural differentpixel accuracies can be selected, the program including a motionprediction/compression step of performing motion prediction/compressionprocessing based on different interpolation methods with respect tointerframe forward predictive encode image and interframe bi-directionalpredictive encoding image.

Here, at the motion prediction compression step, as an interpolationmethod with respect to interframe bi-directional predictive encodingimage, there is selected a method in which operation quantity and thenumber of memory accesses are reduced to more degree as compared tointerframe forward predictive encoding image.

The program according to the present invention includes a picture typediscrimination step of discriminating picture type of image compressedinformation, wherein, at the picture discrimination step, transmissionof command corresponding to interframe forward predictive encoding imageor interframe bi-directional predictive encoding image is performed inaccordance with discrimination result of picture type so that processingat the motion prediction/compensation step is controlled.

Such program allows computer to discriminate picture type of imagecompressed information generated at the image information encodingapparatus to perform motion prediction/compensation processing based oninterpolation method in which operation quantity and the number ofmemory accesses are reduced to more degree as compared to interframeforward predictive encoding image with respect to interframebi-directional predictive encoding image to thereby reduce operationquantity and the number of memory accesses in the motionprediction/compensation processing.

Still more further objects of the present invention and practical meritsobtained by the present invention will become more apparent from thedescription of the embodiments which will be given below with referenceto the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for explaining variable block size of motionprediction/compensation block determined at H.26L.

FIG. 2 is a view for explaining motion prediction/compensationprocessing of 1/4 pixel accuracy determined at the H.26L.

FIG. 3 is a view for explaining bi-directional prediction method using Bpicture at H.26L.

FIG. 4 is a view for explaining PTYPE at H.26L.

FIG. 5 is a view for explaining macro block type determined with respectto B picture at H.26L.

FIG. 6 is a view for explaining Code number of field Blk-size inbi-directional prediction mode.

FIG. 7 is a block diagram for explaining outline of the configuration ofan image information encoding apparatus in the first embodiment of thepresent invention.

FIG. 8 is a block diagram for explaining outline of the configuration ofan image information decoding apparatus in the first embodiment of thepresent invention.

FIG. 9 is a block diagram for explaining outline of the configuration ofan image information encoding apparatus in the second embodiment of thepresent invention.

FIG. 10 is a block diagram for explaining outline of the configurationof an image information decoding apparatus in the second embodimentaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Explanation will now be given with reference to the attached drawings inconnection with practical embodiments to which the present invention isapplied. In this embodiment, the present invention is applied to animage information encoding apparatus adapted for changing an input imagesignal into blocks in accordance with, e.g., H.26L system to implementorthogonal transform thereto on the block basis to perform quantizationthereof to generate image compressed information, and an imageinformation decoding apparatus adapted for inverse-quantizing the imagecompressed information to implement inverse-orthogonal transform theretoto decode such image information.

In the image information encoding apparatus and the image informationdecoding apparatus, as described later, in motionprediction/compensation processing of interframe forward predictiveencoding image (hereinafter referred to as P picture) and interframebi-directional predictive encoding image (hereinafter referred to as Bpicture) where inter-encoding is performed, interpolation methodsdifferent for P picture and B picture are used, thereby making itpossible to reduce operation quantity and the number of memory accesseswhich are required.

First, outline of the configuration of the image information encodingapparatus to which the present invention is applied is shown in FIG. 7.As shown in FIG. 7, the image information encoding apparatus 10 in thisembodiment comprises an A/D converting unit 11, a picture sorting buffer12, an adder 13, an orthogonal transform unit 14, a quantization unit15, a reversible encoding unit 16, a storage buffer 17, aninverse-quantization unit 18, an inverse-orthogonal transform unit 19, aframe memory 20, a motion prediction/compensation unit 21, a picturetype discrimination unit 22, and a rate control unit 23.

In FIG. 7, the A/D converting unit 11 converts an inputted image signalinto a digital signal. Further, the picture sorting buffer 12 performssorting of frames in accordance with GOP (Group of Pictures) structureof image compressed information outputted from the image informationencoding apparatus 10. Here, in regard to intraframe encoding imagewhere intra-encoding is performed (hereinafter referred to as Ipicture), the picture sorting buffer 12 delivers image information ofthe entirety of frame to the orthogonal transform unit 14. Theorthogonal transform unit 14 implements orthogonal transform such asdiscrete cosine transform or Karhunen-Loeve transform, etc. to imageinformation to deliver transform coefficients to the quantization unit15.

The quantization unit 15 implements quantization processing to thetransform coefficients delivered from the orthogonal transform unit 14.

The reversible encoding unit 16 implements reversible encoding such asvariable length encoding or arithmetic encoding, etc. to the quantizedtransform coefficients to deliver the encoded transform coefficients tothe storage buffer 17 to store them thereinto. The encoded transformcoefficients are outputted as image compressed information.

Behavior of the quantization unit 15 is controlled by the rate controlunit 23. Moreover, the quantization unit 15 delivers quantized transformcoefficients to the inverse-quantization unit 18. Theinverse-quantization unit 18 inverse-quantizes those transformcoefficients.

The inverse-orthogonal transform unit 19 implements inverse-orthogonaltransform processing to the inverse-quantized transform coefficients togenerate decoded image information to deliver the information to theframe memory 20 to store them thereinto.

On the other hand, in regard to P pictures and B pictures whereinter-encoding is performed, the picture sorting buffer 12 deliversimage information to the motion prediction/compensation unit 21.Moreover, the picture sorting buffer 12 delivers information of picturetype of frame Picture_type to the picture type discrimination unit 22.The picture type discrimination unit 22 transmits command to the motionprediction/compensation unit 21 on the basis of that information.

At the same time, the motion prediction/compensation unit 21 takes out,from the frame memory 20, image information which is referred toimplement motion prediction/compensation processing by usinginterpolation methods different in P picture and B picture as describedlater on the basis of the command transmitted from the picture typediscrimination unit 22 to generate reference image information.

The motion prediction/compensation unit 21 delivers this reference imageinformation to the adder 13. The adder 13 converts the reference imageinformation into difference signal between the reference imageinformation and the image information. Moreover, at the same time, themotion compensation/prediction unit 21 delivers motion vectorinformation to the reversible encoding unit 16.

The reversible encoding unit 16 implements reversible encodingprocessing such as variable length encoding or arithmetic encoding, etc.to that motion vector information to form information to be insertedinto header portion of image compressed information. It should be notedthat since other processing are similar to processing in the case ofimage compressed information to which intra-encoding is implemented,their explanation will be omitted.

Then, outline of the configuration of the image information decodingapparatus to which the present invention is applied is shown in FIG. 8.As shown in FIG. 8, the image information decoding apparatus 30 in thisembodiment comprises a storage buffer 31, a reversible decoding unit 32,an inverse-quantization unit 33, an inverse-orthogonal transform unit34, an adder 35, a picture sorting buffer 36, a D/A converting unit 37,a motion prediction/compensation unit 38, a frame memory 39, and apicture type discrimination unit 40.

In FIG. 8, the storage buffer 31 temporarily stores inputted imagecompressed information thereafter to transfer it to the reversibledecoding unit 32.

The reversible decoding unit 32 implements processing such as variablelength decoding or arithmetic decoding, etc. to image compressedinformation on the basis of determined format of image compressedinformation to deliver quantized transform coefficients to theinverse-quantization unit 33. In the case where corresponding frame is Ppicture or B picture, the reversible decoding unit 32 also decodesmotion vector information stored in the header portion of imagecompressed information to deliver the information thereof to the motionprediction/compensation unit 38. Further, the reversible decoding unit32 delivers information of picture type of frame Picture_type to thepicture discrimination unit 40. The picture type discrimination unit 40transmits command to the motion prediction/compensation unit 38 on thebasis of that information.

The inverse-quantization unit 33 inverse-quantizes the quantizedtransform coefficients delivered from the reversible decoding unit 32 todeliver transform coefficients to the inverse-orthogonal transform unit34. The inverse-orthogonal transform unit 34 implementsinverse-orthogonal transform such as inverse discrete cosine transformor inverse Karhunen-Loeve transform, etc. to the transform coefficientson the basis of the determined format of image compressed information.

Here, in the case where corresponding picture is I picture, theinverse-orthogonal transform unit 34 delivers inverse-orthogonallytransformed image information to the picture sorting buffer 36. Thepicture sorting buffer 36 temporarily stores this image informationthereafter to deliver it to the D/A converting unit 37. The D/Aconverting unit 37 implements D/A converting processing to the imageinformation to output it.

On the other hand, in the case where corresponding frame is P picture orB picture, the motion prediction/compensation unit 38 takes out, fromthe frame memory 39, image information to be referred to implementmotion prediction/compensation processing by using interpolation methodsdifferent for P picture and B picture as described later on the basis ofreversibly decoded motion vector information and command transmittedfrom the picture type discrimination unit 40 to generate reference imageinformation. The adder 35 synthesizes this reference image and outputfrom the inverse-orthogonal transform unit 34. It should be noted thatsince other processing are similar to processing of intra-encoded frame,its detailed explanation will be omitted.

As described above, the image information encoding apparatus 10 and theimage information decoding apparatus 30 according to the presentinvention perform motion prediction/compensation processing by usinginterpolation methods different in P picture and B picture at motionprediction/compression units 21, 38 on the basis of commands transmittedfrom the picture type discrimination units 22, 40 to thereby reduceoperation quantity and the number of memory accesses which are required.

In view of the above, while motion prediction/compensation at the motionprediction/compensation units 21, 38 will be explained below, sincesimilar processing are performed at the motion prediction/compensationunit 21 and the motion prediction/compensation unit 38, only theprocessing at the motion prediction/compensation unit 21 will beexplained below.

At the motion prediction/compensation unit 21, there are storedinformation relating to two filter coefficients for P picture and Bpicture. The motion prediction/compensation unit 21 implements differentmotion prediction/compensation processing to P picture and B picture bythe first method or the second method indicated below.

First, in the first method, motion prediction/compensation processing ofthe same pixel accuracy is implemented to P picture and B picture. Inthis case, as compared to P picture, filter having lesser number of tapsis used for B picture.

In concrete terms, in the case where motion prediction/compensationprocessing of 1/8 pixel accuracy are performed with respect to both Ppicture and B picture, filter coefficients of 8 taps shown in thefollowing formula (3) are used in regard to P picture, and predictivepicture of 1/8 pixel accuracy is generated by linear interpolation inregard to B picture.1:11/8: {−3, 12, −37, 485, 71, −21, 6, −1}/5122/8: {−3, 12, −37, 229, 71, −21, 6, −1}/2563/8: {−6, 24, −76, 387, 229, −60, 18, −4}/5124/8: {−3, 12, −39, 158, 158, −39, 12, −3}/256  (3)5/8: {−4, 18, −60, 229, 387, −76, 24, −6}/5126/8: {−1, 6, −21, 71, 229, −37, 12, −3}/2567/8: {−1, 6, −21, 71, 485, −37, 12, −3}/512

Moreover, in the case where motion prediction/compensation processing of1/4 pixel accuracy is performed with respect to both P picture and Bpicture, filter coefficients of 8 taps as shown in the following formula(4) are used with respect to respective phases in regard to P picture togenerate predictive picture of 1/4 pixel accuracy. On the other hand, inregard to B picture, filter coefficients of 6 taps shown in thefollowing formula (5) are used to generate predictive picture of 1/2pixel accuracy, and predictive picture of 1/4 pixel accuracy isgenerated by linear interpolation.1/4: {−3, 12, −37, 229, 71, −21, 6, −1}/2562/4: {−3, 12, −39, 158, 158, −39, 12, −3}/256  (4)3/4: {−1, 6, −21, 71, 229, −37, 12, −3}/256{1, −5, 20, 20, −5, 1}/32  (5)

It is to be noted that, in regard to B picture, predictive picture of1/4 pixel accuracy may be generated by linear interpolation to performmotion prediction/compensation processing.

Moreover, in regard to P picture, filter coefficients of 6 taps show inthe formula (5) may be used to generate predictive pixel of 1/2 pixelaccuracy thereafter to generate predictive picture of 1/4 pixel accuracyby linear interpolation. In regard to B picture, predictive picture of1/4 pixel accuracy may be generated by linear interpolation to performmotion prediction/compensation processing.

Then, in the second method, there is performed motionprediction/compensation processing having higher accuracy with respectto P picture as compared to B picture.

In concrete terms, in regard to P picture, filter coefficients of 8 tapsshown in the above-described formula (3) are used to generate predictivepicture of 1/8 pixel accuracy to perform motion prediction/compensationprocessing. On the other hand, in regard to B picture, filtercoefficients of 6 taps shown in the above-described formula (5) are usedto generate predictive picture of 1/2 pixel accuracy to generatepredictive picture of 1/4 pixel accuracy by linear interpolation toperform motion prediction/compensation processing. It is to be notedthat, in regard to B picture, predictive picture of 1/4 pixel accuracymay be generated, or predictive picture of 1/2 pixel accuracy mat begenerated by linear interpolation to perform motionprediction/compensation processing.

Moreover, in regard to P picture, filter coefficients of 6 taps shown inthe formula (5) may be used to generate predictive picture of 1/2 pixelaccuracy thereafter to generate predictive picture of 1/4 pixel accuracyby linear interpolation. In regard to B picture, predictive picture of1/2 pixel accuracy may be generated by linear interpolation to performmotion prediction/compensation processing.

Then, another example of the image information encoding apparatus 50according to the present invention is shown in FIG. 9. The imageinformation encoding apparatus 50 shown in FIG. 9 has the fundamentalconfiguration similar to the image information encoding apparatus 10shown in FIG. 7. In this example, the image information encodingapparatus 50 is characterized in that it includes a motionprediction/compensation unit (fixed filter) 51, and a motionprediction/compensation unit (adaptive filter) 52, wherein use of anyone of filters is switched by a switching unit 54 in accordance withcommand from a picture type discrimination unit 53. Namely, the imageinformation encoding apparatus 50 includes, as components thereof, asingle motion prediction/compensation unit 21 like the image informationencoding apparatus 10 in the above-described first embodiment, andincludes, as components thereof, two components of motionprediction/compensation unit (fixed filter) 51 as prescribed at presentin the H.26L, and motion prediction/compensation unit (adaptive filter)52 as proposed in the previously described literature 1 without havingfilter coefficients for P picture and B picture therewithin, whereby anyone of filters is used in dependency upon P picture or B picture.

Moreover, image information decoding apparatus 70 shown in FIG. 10 hasthe fundamental configuration similar to the image information decodingapparatus 30 shown in FIG. 8, and is characterized in that it includes amotion prediction/compensation unit (fixed filter) 71, and a motionprediction/compensation unit (adaptive filter) 72, wherein whether ornot either one of these filters is used is switched by a picturediscrimination unit 73 in accordance with command from a picturediscrimination unit 73.

Accordingly, since the same reference numeral are respectively attachedto the configurations similar to those of the image information encodingapparatus and the image information decoding apparatus 30 previouslyshown in FIGS. 7 and 8, their explanation will be omitted.

In the image information encoding apparatus 50 shown in FIG. 9, picturesorting buffer 12 delivers information of picture type of framePicture_type to picture type discrimination unit 53. The picture typediscrimination unit 53 transmits command to the switching unit 54 on thebasis of that information.

Namely, in the case where corresponding frame is B picture, theswitching unit 54 is switched to the side of a in the figure by theabove-described command. Thus, motion prediction/compensation processingby the fixed filter is performed by using motion prediction/compensationunit (fixed filter) 51.

On the other hand, in the case where corresponding frame is P picture,the switching unit 54 is switched to the side of b in the figure by theabove-described command. Thus, motion prediction/compensation processingby the adaptive filter is performed by using the motionprediction/compensation unit (adaptive filter). In more detail,initially, as the first step, motion vector d(k) which minimizespredictive error is determined by using filter determined in advance.Subsequently, as the second step, such filter coefficients H(k) tominimize predictive error are determined with respect to motion vectord(k) determined at the first step. Further, motion compensationprocessing is performed by the filter coefficients H(k) and the motionvector d(k) which have been determined in this way. Information relatingto the filter coefficients are transmitted in the state embedded inimage compressed information. In this instance, variable length encodingprocessing or arithmetic encoding processing may be implemented at thereversible encoding unit 16 to compress information quantity thereafterto embed such information into image compressed information.

It is to be noted that pixel accuracy in motion prediction/compressionprocessing at the motion prediction/compensation unit (fixed filter) 51or motion prediction/compensation unit (adaptive filter) 52 of P pictureand that of B picture may be equal to each other, and motionprediction/compression processing of higher pixel accuracy may beperformed with respect to P picture as compared to B picture.Transmission of information of pixel accuracy is performed in the stateembedded in MotionResolution field at RIP (Real-time Transfer Protocol)layer within image compressed information to be outputted.

In the image information decoding apparatus 70 shown in FIG. 10,reversible decoding unit 32 delivers information of picture type offrame Picture_Type to picture type discrimination unit 73. The picturetype discrimination unit 73 transmits command to switching unit 74 onthe basis of that information.

Namely, in the case where corresponding frame is B picture, theswitching unit 74 is switched to the side of c in the figure by theabove-described command. Thus, predictive mode information and motionvector information are delivered the motion prediction/compensation unit(fixed filter) 71. As a result, motion prediction/compensationprocessing by fixed filter is performed on the basis of theseinformation.

On the other hand, in the case where corresponding frame is P picture,the switching unit 74 is switched to the side of d in the figure by theabove-described command. Thus, information relating to filtercoefficients is delivered to motion prediction/compensation unit(adaptive filter) 72 along with predictive mode information and motionvector information. As a result, motion prediction/compensationprocessing by the adaptive filter is performed on the basis of theseinformation.

In this example, at the motion prediction/compensation unit (fixedfilter) 71 or the motion prediction/compensation unit (adaptive filter)72, motion prediction/compression processing is performed on the basisof pixel accuracy embedded in MotionResolution field at RTP layer withinimage compressed information.

As explained above by using the first and second embodiments, motionprediction/compression processing based on different interpolationmethods are performed with respect to P picture and B picture, therebymaking it possible to reduce operation quantity and the number of memoryaccesses at B picture for which a larger operation quantity and thenumber of memory accesses are required as compared to P picture whilesuppressing deterioration in picture quality as minimum as possible.

It should be noted that the present invention is not limited only to theabove-described embodiments, it is a matter of course that variouschanges or modifications may be made within the range which does notdepart from the gist of the present invention.

For example, while the present invention has been explained as theconfiguration of hardware in the above-described embodiments, thepresent invention may be also realized, without being limited to suchimplementations, by allowing CPU (Central Processing Unit) torespectively execute processing at image information encodingapparatuses 10, 50 and image information decoding apparatuses 30, 70.

It is to be noted that the invention has been described in accordancewith preferred embodiments thereof illustrated in the accompanyingdrawings and described in the above description in detail, it should beunderstood by those ordinarily skilled in the art that the invention isnot limited to embodiments, but various modifications, alternativeconstructions or equivalents can be implemented without departing fromthe scope and spirit of the present invention as set forth by appendedclaims.

INDUSTRIAL APPLICABILITY

As described above, in accordance with the image information encodingapparatus and the image information encoding method according to thepresent invention, picture type of input image signal is discriminatedto perform, with respect to interframe bi-directional predictiveencoding image, motion prediction/compensation processing based oninterpolation method in which operation quantity and the number ofmemory accesses are reduced to more degree as compared to interframeforward predictive encoding image, thereby making it possible to reduceoperation quantity and the number of memory accesses in motionprediction/compensation processing.

Moreover, the program according to the present invention is used tothereby allow computer to discriminate picture type of input imagesignal to perform motion prediction/compensation processing based oninterpolation method in which operation quantity and the number ofmemory accesses are reduced to more degree as compared to interframeforward predictive encoding picture with respect to interframebi-directional predictive encoding image, thereby making it possible toreduce operation quantity and the number of memory accesses in motionprediction/compensation processing.

In accordance with the image information decoding apparatus and theimage information decoding method according to the present invention,picture type of image compressed information generated at the imageinformation encoding apparatus is discriminated to perform motionprediction/compensation processing based on interpolation method inwhich operation quantity and the number of memory accesses are reducedto more degree as compared to interframe forward predictive encodingimage with respect to interframe bi-directional predictive encodingimage, thereby making it possible to reduce operation quantity and thenumber of memory accesses in motion prediction/compensation processing.

Further, another program according to the present invention is used tothereby allow computer to discriminate picture type of image compressedinformation generated at the image information encoding apparatus toperform motion prediction/compensation processing based on interpolationmethod in which operation quantity and the number of memory accesses arereduced to more degree as compared to interframe forward predictiveencoding image with respect to interframe bi-directional predictiveencoding image, thereby making it possible to reduce operation quantityand the number of memory accesses in motion prediction/compensationprocessing.

The invention claimed is:
 1. An image information decoding apparatus fordecoding, by inverse-orthogonal transform and motion compensation, animage compressed information at least including intraframe encodingimage, interframe forward predictive encoding image and interframebi-directional predictive encoding image which have been generated at animage information encoding apparatus, the image information decodingapparatus including a processor comprising: a motion compensation unitconfigured to perform, at the processor of the image informationdecoding apparatus, motion compensation processing by using a firstfilter with respect to the interframe forward predictive encoding image,wherein the motion compensation unit performs interpolation processingof 1/2 pixel accuracy by using the first filter having 8 taps andperforming interpolation processing of 1/4 pixel accuracy by anotherfilter having 8 taps, and the motion compensation unit performs motioncompensation processing by using a second filter having a fewer numberof taps than the first filter, with respect to the interframebi-directional predictive encoding image.
 2. An image informationdecoding method for decoding, by inverse-orthogonal transform and motioncompensation processing, image compressed information at least includingintraframe encoding image, interframe forward predictive encoding imageand interframe bi-directional predictive encoding image which have beengenerated at an image information encoding apparatus, the imageinformation decoding method comprising: performing motion compensationprocessing by using a first filter with respect to the interframeforward predictive encoding image, wherein the performing motioncompensation processing includes performing interpolation processing of1/2 pixel accuracy by using the first filter having 8 taps andperforming interpolation processing of 1/4 pixel accuracy by anotherfilter having 8 taps, and the motion compensation processing includesperforming motion compensation processing by using a second filterhaving a fewer number of taps than the first filter with respect to theinterframe bi-directional predictive encoding image.
 3. A non-transitorycomputer-readable storage medium having embedded therein instructions,which when executed by a processor, cause the processor to perform amethod of decoding information, by inverse-orthogonal transform andmotion compensation processing, image compressed information at leastincluding intraframe encoding image, interframe forward predictiveencoding image and interframe bi-directional predictive encoding imagewhich have been generated at an image information encoding apparatus,the method comprising: performing motion compensation processing byusing a filter with respect to the interframe forward predictiveencoding image, wherein the performing motion compensation processingincludes performing interpolation processing of 1/2 pixel accuracy byusing the first filter having 8 taps and performing interpolationprocessing of 1/4 pixel accuracy by another filter having 8 taps, andthe motion compensation processing includes performing motioncompensation processing by using a second filter having a fewer numberof taps than the first filter, with respect to the interframebi-directional predictive encoding image.